It is common practice to increase the strength of the overhangs of header plates used on pressure vessels and heat exchangers by adding rib patterns to the plates rather than increasing their gage (thickness). For example, the typical header on a motor vehicle radiator made of aluminum with flat sided tubes has a plurality of bumps formed in the header each with a pierced tube slot. The latter provides a joint surface for the tube header joint, lead in to assist or guide inserting the tube into the tube slot and increased header stiffness in the tube to header joint area. The tank is attached to the header by means of a gasketed clinch joint or brazing and the region between the tube bumps and the tank to header clinch joint is referred to as the header overhang. And it is the header overhang that is subjected to bending loads resulting from internal pressure in the radiator with such bending loads increasing proportionally with the length of the overhang and the resulting deformations increasing with the cube of the length of the overhang. Thus, radiators utilizing a large overhang would require heavy gage headers to resist the resulting bending loads. For this reason, and to avoid increasing the header gage, ribs ar formed in the header overhang region to increase the header strength and thereby minimize the header gage required. Normally, such ribs are located between the tube slots and formed in the opposite direction of the tube bumps. That is, the tube bumps normally project upward from the liquid side of the header plate and the reinforcement ribs project in the opposite direction from the air side of the header plate. While this has proven generally satisfactory, the degree of ribbing possible is controlled by the formability of the header material. For example, such conventional ribbing works well for moderate overhang lengths but can be only marginally effective with the large overhangs required by some applications where the width of the tank is substantially greater than the corresponding dimension of the flat tubes.